The present invention relates to a method of making a metallic container, and more particularly to a method of making a metallic container having a circumferential seam bonded with an adhesive layer.
In FIG. 1 there is illustrated a metallic container 1 of the type to which the method of the invention will be applied. The metallic container 1 is formed by telescoping the necked-in open end portion 3b of a relatively thin-walled lower can body 3 having a bottom portion 3a into the open end portion 2b of a relatively thin-walled upper can body 2 having a venting portion 2a, with an adhesive layer 4 interposed therebetween, and heating the fitted portion thus formed to the heat sealable temperature of the plastic forming the adhesive layer 4, thereby forming a circumferential seam 5.
In case where the metallic container 1 is sealed by clinching the venting portion 2a with a metallic cap 6 by using a clincher not shown, when the heights of the containers 1 are not uniform, the following difficulties are often encountered. The container 1 having a height smaller than the standard value tends to fail to be hermetically sealed, and the container 1 having a height larger than the standard value tends to be buckled at its sidewall portion 1a, resulting in a container having no commercial value, since the distance between a mounting plate not shown for the container 1 and the pawls (not shown) of the clincher is constant regardless of the variation of the height of the container 1.
In the process of making the container 1, while the container preform is transferred from a telescoping apparatus to an apparatus for heating the fitted portion, the fitted portion is liable to axial slip, or the upper can body 2 tends to tilt with respect to the lower can body 3. Accordingly, even if the container preforms as telescoped are uniform in height, it is difficult to obtain containers 1 having a uniform height by merely heating the fitted portion.
Furthermore, relatively thin-walled open end portions 2b and 3b, e.g., having the thickness of 0.15 to 0.30 mm often fail to form a round fitted portion. Therefore, in case where the fitted portion is heated by means of a heating means such as a high frequency induction heating coil, the circumferential space between the fitted portion and the heating means tends to become uneven, and thus the heating along the fitted portion tends to be not uniform. As a result there is often formed the circumferential seam 5 in which air- or liquid-tightness is poor owing to imperfect heat fusion of the adhesive layer 4 by shortage of heating, or a burnt primer coating thereon by overheating.